As a facility for continuous casting of molten metal, there is known a continuous casting machine having an endless-travelling type mold which comprises a plurality of endlessly connected metal blocks or an endless-travelling type mold which comprises an endless metal belt.
FIG. 1 is a schematic side view illustrating a conventional continuous casting machine having an endless-travelling type mold. In FIG. 1, 4 is an endless-travelling type mold; and 2 is a wall member forming part of the endless-travelling type mold. The wall member 2 comprises a plurality of endlessly connected metal blocks 5 and a pair of sprockets 12. The plurality of endlessly connected blocks 5 are stretched between the pair of sprockets 12. The wall member 2 comprising the plurality of endlessly connected blocks 5 travels endlessly by the action of a driving device (not shown) provided on at least one of the pair of sprockets. A pair of wall members 2 having the construction as described above are arranged one above the other with a prescribed distance therebetween as shown in FIG. 1. More specifically, the pair of wall members 2 are vertically opposed to each other. Although not shown in FIG. 1, another pair of wall members having the same construction as the pair of vertically opposed wall members 2, are arranged with a prescribed distance therebetween on the both sides of the pair of vertically opposed wall members 2. More specifically, the another pair of wall members are horizontally opposed to each other. The pair of vertically opposed wall members 2 and the another pair of horizontally opposed wall members travel endlessly toward the downstream in the same direction and at the same speed. Thus, the above-mentioned two pairs of wall members form the endless-travelling type mold (hereinafter simply referred to as the "mold") 4. The mold 4 is usually installed at a prescribed downward inclination angle toward the downstream.
As shown in FIG. 1, upstream end of a conventional molten metal pouring nozzle 10 made of a refractory is connected to a lower portion 11a of a side wall of a tundish 11, and the downstream end of the molten metal pouring nozzle 10 is inserted into an inlet of the above-mentioned mold 4.
Molten metal received in the tundish 11 is continuously poured into the mold 4 through a bore of the pouring nozzle 10. The above-mentioned two pairs of wall members 2 forming the mold 4 are forcedly cooled by means of a cooling device (not shown). Molten metal 8 poured into the mold 4 is therefore solidified into a cast metal strand 9 in the mold 4. The cast metal strand 9 is continuously moved toward the downstream by the action of the endlessly travelling mold 4. The cast metal strand 9 is then squeezed and withdrawn from the mold 4 by means of at least one pair of pinch rolls 13 which rotate synchronously with the travelling speed of the endlessly travelling mold 4, whereby the cast metal strand 9 is continuously cast.
However, when continuously casting the cast metal strand 9 by the use of the conventional molten metal pouring nozzle 10, the following problems are encountered.
FIG. 2 is a partial sectional view illustrating a conventional molten metal pouring nozzle 10, the downstream end of which is inserted into the inlet of an endless-travelling type mold. In FIG. 2, the arrow indicates the flow direction of molten metal 8 in the mold. Molten metal 8 poured into the mold through the bore of the pouring nozzle 10 is cooled and solidified by the wall members 2 each comprising the plurality of endlessly connected metal blocks 5, and a solidified shell 6 is formed along the surface of the wall member 2 of the mold. At this time, a basic end portion 6a of the solidified shell 6 is firstly formed at a corner formed by the downstream end face 10a of the pouring nozzle 10 and the surface of the wall member 2. The basic end portion 6a of the solidified shell 6 tends to easily adhere to the downstream end face 10a of the pouring nozzle 10. Therefore, a tensile strain is produced in the solidified shell 6 of the cast metal strand 9, when the solidified shell 6 is pulled toward the downstream by the endlessly travelling wall members 2, thus resulting in occurrence of such defects as cracks and flaws on the surface of the cast metal strand 9. Sometimes, the basic end portion 6a of the solidified shell 6 is cut off from the body of the solidified shell 6, and the thus cut-off basic end portion 6a is entrapped into molten metal 8 in the mold, thus causing deterioration of the quality of the cast metal strand 9. Furthermore, the downstream end portion of the pouring nozzle 10, to which the basic end portion 6a of the solidified shell 6 has adhered, is pulled by the solidified shell 6 moving toward the downstream, and as a result, the downstream end portion of the pouring nozzle 10 may be broken. Pieces of the broken pouring nozzle 10 are entrapped into molten metal in the mold, thus causing deterioration of the quality of the cast metal strand 9. In addition, the pouring nozzle 10, if used as broken, may result in such a danger as leakage of molten metal 8 from the broken portion of the pouring nozzle 10, thus interrupting the casting operation.
Adhesion of the basic end portion 6a of the solidified shell 6 to the downstream end face 10a of the molten metal pouring nozzle 10, exerts adverse effects on the continuous casting operation as described above. There is therefore a strong demand for the development of a molten metal pouring nozzle for a continuous casting machine having an endless-travelling type mold, in which a basic end portion of a solidified shell of a cast metal strand never adheres to the downstream end face of the pouring nozzle, but such a pouring nozzle has not as yet been proposed.